The present invention relates to a master optical disk heat-drying apparatus in which a master optical disk is radiation-heated with a far-infrared or infrared heater.
A conventional heat-drying apparatus, known as a heat tunnel, is shown in FIGS. 1(A) and 1(B). In such a heat-drying apparatus, a material to be heated (hereinafter referred to "objective material") 61 is conveyed by a belt conveyor 62 into a tunnel constituted by a plurality of heaters 63 to heat-dry the objective material 61 by thermal conduction due to tunnel temperature while the objective material is passed through the tunnel.
However, such a heat-drying apparatus is deficient, for the following reasons. The apparatus is arranged such that the objective material 61 is placed on the belt conveyor 62 on the opposite side of the apparatus from that where the objective material 61 is withdrawn from the apparatus. Accordingly, in the case where there is only one operator to perform both the insertion and the withdrawal, and the objective material is a master optical disk, workability is exceedingly poor because the apparatus is large, and because close attention must be paid to treatment of the master disk.
There is another reason that such a heat-drying apparatus is deficient. The apparatus is arranged such that the objective material 61 is mounted with its surface to be heated facing up on the belt conveyor 62, so that the surface to be heated is heated from above. Accordingly, in the case where the objective material 61 is a master optical disk, there is a risk that the surface of the master optical disk to be heated may become contaminated with impurities, such as particles or the like falling on the surface by gravity. Consequently it is necessary to take steps to prevent such contamination.
The heat-drying apparatus has still another defect in that control of temperature distribution on the surface of the objective material 61 to be heated cannot be carried out, because the temperature distribution depends on the heat capacity of the heaters 63, the conveying speed of the belt conveyor 62, and the thermal characteristics and shape of the objective material 61.
Since heating is performed through thermal conduction due to atmospheric temperature in the tunnel, the temperature on the surface of the objective material 61 to be heated is unevenly distributed over the whole surface, that is, the surface temperature is low in the central and outermost peripheral portions and high in an intermediate portion. For an optical recording glass master disk with one surface coated with a photoresist, the surface temperature of the glass master disk increases, up to a point, as a function of radial position from the inner circumference toward the outer circumference, but then decreases so as to become lower at the outermost circumference, as shown in the graph (c) in FIG. 2. Thus, if the temperature in a heat-drying process varies, the sensitivity of the photoresist also varies, thereby affecting the shapes of pits by which information is recorded. Further, it has been confirmed by the inventor that if the heating temperature at the outermost peripheral portion is low the glass master disk is likely to break.
FIG. 3 shows a conventional heat-drying apparatus in which temperature distribution can be controlled. This heat-drying apparatus is arranged such that an objective material 61 is heat-dried by heaters 63' which are arranged at varying distances from the objective material 61. In this case, the heat-drying treatment can be performed even if the objective material 61 is moving, rotating, or standing still.
In this heat-drying apparatus, the temperature distribution can be controlled to a certain extent. However, this apparatus is deficient in that space utilization is poor. This is because the temperature distribution is controlled on the basis of the distance between each heater 63 and the objective material 61, and depending on the size of the objective material 61 it becomes impossible to control the temperature distribution because of the relation between the size of the material and the size of the heaters 63'.